Linezolid, i.e. [(S)—N-[[3-(3-fluoro-4-morpholinyl)phenyl]-2-oxo-5-oxazolidinyl]methyl]acetamide], having the following formula
is an antibacterial agent, whose preparation is disclosed in WO 95/07271. Various polymorphic forms of linezolid are known, for example, U.S. Pat. No. 6,559,305 claims a linezolid crystalline form referred to as Form II. According to this document, another crystalline form is known from J. Med. Chem., 39(3), 673-679 (1996), also referred to as Form I.
US 2006/0142283 claims a crystalline Form IV, also claimed by WO 2005/035530 but as crystalline Form III, which is stated to be more compact and less electrostatic than the Form II. US 2006/0111350 discloses various polymorphic forms and claims linezolid in the hydrate form. Finally, WO 2007/026369 discloses the amorphous form of linezolid.
It is well known that the physical properties of a drug are fundamental for the preparation of pharmaceutical forms in pharmaceutical technique. In particular, solid drugs characterized by not very dense, highly electrostatic crystals are difficult to mill. A further important characteristic is the flowability of the powders resulting from the milling of the solid: in fact, when the powdered compound particles do not flow, they stick to one another. A further important aspect, which is affected by the crystalline structure of the product, is its dissolution rate in aqueous fluids, hence its bioavailability.
There is therefore the need for a novel linezolid crystalline form and linezolid salts, having more advantageous characteristics for use in the pharmaceutical technique and in clinics.